代码

int binary_search(const unsigned *a, int n, unsigned x)
{
    static int lastid = 0;
    static int last = a[0];
    int l = -1, r = n;
    if (last > x)
    {
        r = lastid;
    }
    else if (last < x)
    {
        l = lastid;
    }
    else
    {
        return lastid;
    }

    while (l + 1 < r)
    {
        int mid = (l + r) / 2;
        if (a[mid] < x)
        {
            l = mid;
        }
        else
        {
            r = mid;
        }
    }
    return l + 1;
}

评测结果